1. Field of the Invention
The present invention relates to a hydraulic valve assembly installed in a hydraulic working machine and a method for assembling the same.
2. Description of the Related Art
Control valves used in a hydraulic excavator are usually divided into two groups, which are installed into two separate main valve blocks. In both main valve blocks, there are respectively disposed pressure oil supply passages for conducting pressure oil from first and second pumps as pressure oil sources in the main valve blocks to the control valves.
In addition to a standard specification, an option attachment such as a crusher or a breaker is sometimes attached to the hydraulic excavator. In this case, an option actuator for the option attachment and an option valve for controlling the operation of the option actuator are needed.
In a method wherein an option valve unit comprising the option valve and a circuit element connected hydraulically to the option valve unit is installed into a main valve block, the option actuator is connected to an actuator port formed in the main valve block.
An affixing method wherein a connection block with an option valve and a related circuit element incorporated therein is attached to a main valve block is disclosed, for example, in Japanese Unexamined Patent Publication No. Hei 10-25770.
However, in the former method, since there is obtained only one function that the built-in option valve unit possesses, it is impossible to cope with various option attachments different in function and purpose of use. For example, in the case where an actuator for an option attachment requires a large flow rate, it has so far been impossible to meet various users' demands, including a demand for joining discharge oil from both pumps and feeding the resulting confluent oil to an option actuator and a demand for limiting pressure due to a low working pressure of an option actuator.
On the other hand, according to the latter affixing method, since an option valve and a related circuit element are integrated to constitute a connection block, connection blocks with option valve must be provided and replaced by the number corresponding to the number of required functions (circuit elements). Consequently, not only the cost is very high but also the connection blocks are large-sized and heavy, thus giving rise to the problem that the replacing work is troublesome.